1. Field of The Invention
This invention relates to an aluminium alloy having an excellent forgeability and more particularly to an aluminium alloy suitable to make a piston for an internal-combustion engine.
2. Description of the Prior Art
Conventionally, in the field of aluminium alloy working technology for producing pistons for internal-combustion engines, a casting method has been known.
Recently, however, a powder metallurgical method attracts a good deal of attention instead of the conventional casting method.
The reason for this tendency is that the powder metallurgical method can give a wider range of selection of added elements as compared with the casting method. According to this powder metallurgical method, it is preferable to use a consolidated rapid-quenched aluminium alloy powder. The consolidated rapid-quenched aluminium alloy powder employed in the above metallurgical method is made by rapidly quenching a molten aluminium alloy at cooling rates of 10.sup.3 -10.sup.7 .degree.C./sec. which are 10.sup.2 -10.sup.5 times faster than those of the conventional aluminium alloy casting.
Consequently, the solid solution of the alloying elements of the consolidated rapid-quenched aluminium alloy powder in the metallurgical method is highly oversaturated. Therefore, the aluminium alloy product which is made of the consolidated rapid-quenched aluminium alloy powder has excellent mechanical characteristics, such as a superior abrasion resistance and high-temperature resistance unobtainable by conventional aluminium alloy casting. The Japanese Unexamined published patent application No. 131945/1985, for instance, discloses a technique for making aluminium alloy products by such a metallurgical method.
According to such an aluminium alloy product as disclosed in the Japanese Unexamined published patent application No. 131945/1985, there are cases where cracks develop on the product when it is made by forging. It is conceived that such cracks may have been caused by insufficient flexibility of the forged aluminium alloy product.